Export thread

Briggs 3hp Carb (397939) running rough..help..

#1

H

hatteras451

Could anyone help me with a carb problem...I have a Briggs 3hp on a Mclane edger. Carb part no. 397939. It has not ran smooth since I purchased it used. I have taken it apart and soaked in carb cleaner, blown out with compressor, put a new kit on (twice) and adjusted mixture screw. First, it is hard to get started. Most of the time I need starter fluid to get going. After warmed up, it cranks fine but runs very rough. It surges and sounds like it wants to cut off. Runs like there may be trash in it but I have cleaned it twice along with the soaking. Or either the mix id off which I have played with for quite a while. Is there anything else I can look at when I take it back off? Thanks


#2

R

Rivets

Please post the engine model numbers, which may help us.


#3

Carscw

Carscw

hatteras451 said:
Could anyone help me with a carb problem...I have a Briggs 3hp on a Mclane edger. Carb part no. 397939. It has not ran smooth since I purchased it used. I have taken it apart and soaked in carb cleaner, blown out with compressor, put a new kit on (twice) and adjusted mixture screw. First, it is hard to get started. Most of the time I need starter fluid to get going. After warmed up, it cranks fine but runs very rough. It surges and sounds like it wants to cut off. Runs like there may be trash in it but I have cleaned it twice along with the soaking. Or either the mix id off which I have played with for quite a while. Is there anything else I can look at when I take it back off? Thanks
Click to expand...

When you rebuilt the carb did you change out the welch plug?

Take it easy with the starting fluid it can do piston damage.

(( cowboy up and get over it ))


#4

H

hatteras451

Carscw said:
When you rebuilt the carb did you change out the welch plug?

Take it easy with the starting fluid it can do piston damage.

(( cowboy up and get over it ))
Click to expand...

it has been awhile but i finally started playing with this carb again...no i have not changed out the welch plug...today i found out something new about the issue...i dont know if it has anything to do with the problem but twice i noticed just before running out of gas..about 3-5 minutes before cutting off, it ran just as smooth as you could ask for...after putting some gas in, it starts back with the rough running...i have gotten the surge out and do not need to use starter fluid any longer but it just sounds terrible...but just before running completely out of gas, it runs fine...could this be a welch plug issue?..i have inserted a picture of the carb for reference...thanks...DSCN1100.jpg


#5

R

Rivets

All you need is an adjustment which you can do yourself. Start up the unit with the air cleaner on and run it at full throttle. While it is running slowly turn the fuel adjusting screw on the side of the carb in until it runs smooth. Continue to turn the screw in until it starts to bog down and then turn the screw out 1/8 turn. Stop, should solve your problem.


#6

silver1

silver1

hatteras451 said:
it has been awhile but i finally started playing with this carb again...no i have not changed out the welch plug...today i found out something new about the issue...i dont know if it has anything to do with the problem but twice i noticed just before running out of gas..about 3-5 minutes before cutting off, it ran just as smooth as you could ask for...after putting some gas in, it starts back with the rough running...i have gotten the surge out and do not need to use starter fluid any longer but it just sounds terrible...but just before running completely out of gas, it runs fine...could this be a welch plug issue?..i have inserted a picture of the carb for reference...thanks...View attachment 20281
Click to expand...

Well the picture shows a governor spring that is not in good shape. It should be attached to the loop in the throttle linkage.
Did you replace the diaphragm on the other side of the carb.? They can get damaged by Ethanol in the gas. If your gas tank has
any crude in it that can make fuel pickup problems.


#7

H

hatteras451

silver1 said:
Well the picture shows a governor spring that is not in good shape. It should be attached to the loop in the throttle linkage.
Did you replace the diaphragm on the other side of the carb.? They can get damaged by Ethanol in the gas. If your gas tank has
any crude in it that can make fuel pickup problems.
Click to expand...

I have replaced the governor spring. That photo was actually taken while waiting on the spring to arrive. I did replace the diaphragm on the first round of service. I actually have taken it back out again since to clean again thinking I may have missed something. I replaced the throttle cable yesterday along with all gaskets again. I am doing things 2 and 3 times because I am out of ideas. Carscw suggested replacing the welch plug which I have ordered and waiting on it to arrive. After I replace that, I will definately be out of ideas. Thanks for your suggestions.


#8

H

hatteras451

Rivets said:
All you need is an adjustment which you can do yourself. Start up the unit with the air cleaner on and run it at full throttle. While it is running slowly turn the fuel adjusting screw on the side of the carb in until it runs smooth. Continue to turn the screw in until it starts to bog down and then turn the screw out 1/8 turn. Stop, should solve your problem.
Click to expand...

I have been adjusting the mixture screw with no luck getting it to that smooth point. I just went out and put the air cleaner back on as you suggested and played with it again but with no luck. I have cleaned the screw and jet multiple times but I have not replaced them. I did pull a screw and jet from another carb just the same and installed but with the same results. Frustrated....Thanks for your suggestion!


#9

silver1

silver1

hatteras451 said:
I have been adjusting the mixture screw with no luck getting it to that smooth point. I just went out and put the air cleaner back on as you suggested and played with it again but with no luck. I have cleaned the screw and jet multiple times but I have not replaced them. I did pull a screw and jet from another carb just the same and installed but with the same results. Frustrated....Thanks for your suggestion!
Click to expand...

I had a 2 Hp that the head was FULL of carbon and it ran poorly until I cleaned it out. It had the same carb.


#10

R

Rivets

You have an adjustable Pulsa-Jet carb. Take a look at section 3 of this manual, which may give you some help. Page 17, figure 31. shows the pump assembly and the rest of the section may give you some clues. This carb is very simple, I can't understand why we can't figure it out.


#11

I

ILENGINE

this may or may not be relevant. Do you have a way to do a compression test. I am wondering if this issue may be more compression related, then carb related. Low compression causing improper ignition of fuel in the cylinder. those small L head briggs engines were bad to float the intake valve.


#12

J

jsm0960

hatteras451 said:
Could anyone help me with a carb problem...I have a Briggs 3hp on a Mclane edger. Carb part no. 397939. It has not ran smooth since I purchased it used. I have taken it apart and soaked in carb cleaner, blown out with compressor, put a new kit on (twice) and adjusted mixture screw. First, it is hard to get started. Most of the time I need starter fluid to get going. After warmed up, it cranks fine but runs very rough. It surges and sounds like it wants to cut off. Runs like there may be trash in it but I have cleaned it twice along with the soaking. Or either the mix id off which I have played with for quite a while. Is there anything else I can look at when I take it back off? Thanks
Click to expand...

Have you done a compression test on it?


#13

R

Rivets

Sorry I forgot the manual.

http://dl.dropboxusercontent.com/u/12502267/B&S Service Manuals/01_270962SingleCylinderLHead.pdf


#14

T

tomsteve

along with what others have said about compression and carbon build up, spray some carb cleaner around the gaskets while running and see if it smooths out. it could be a gasket leak,too.


#15

H

hatteras451

silver1 said:
I had a 2 Hp that the head was FULL of carbon and it ran poorly until I cleaned it out. It had the same carb.
Click to expand...

Thanks for the suggestion!..I may have to look into checking that...


#16

H

hatteras451

tomsteve said:
along with what others have said about compression and carbon build up, spray some carb cleaner around the gaskets while running and see if it smooths out. it could be a gasket leak,too.
Click to expand...

I have replaced the gasket twice. I did have an issue with fuel leaking around one side on the previous gasket. Do you think it would be fine to try 2 gaskets? Thanks..


#17

H

hatteras451

Rivets said:
Sorry I forgot the manual.

http://dl.dropboxusercontent.com/u/12502267/B&S Service Manuals/01_270962SingleCylinderLHead.pdf
Click to expand...

Thanks for the manual breakdown!...I am going to disassemble it again and make sure everything is in place and clean...once again...


#18

Fish

Fish

Is there any chance you can give all of the model/type/code numbers, which are almost readable in your pic?


#19

Fish

Fish

Before all of my "haters" start pile driving me, I just would like to know what the date code was, so I could know whether or not you need to change your point ignition over to electronic.......


#20

Fish

Fish

While still waiting for the model/type/code numbers, another problem with these engines had, when the carb is removed, the carb has/had a downspout/pipe into the tank near the bottom, and many of the tanks had a small cup/bowl up where the carb bolted
on, and the bowl served as a normal carb bowl. But after a few decades of sitting with old fuel/water, this small cup/bowl gets
rusted up, and develops rust pin holes in the cup, and the gas seeps back into the tank, and after a while makes it real hard to start, as it gets the startup gas from this bowl. Also, if the leak is bad enough, will affect the running of the engine.

But as I said earlier, we need to know which model you have.


#21

H

hatteras451

Fish said:
Is there any chance you can give all of the model/type/code numbers, which are almost readable in your pic?
Click to expand...

Model: 80202
Type: 1765
Code: 91091603


Thanks..


#22

Fish

Fish

OK no points, but did you look at the bowl on the tank? Rust?


#23

M

mechanic mark

http://www.briggsandstratton.com/~/...on_troubleshooting_detail_reference_guide.pdf


#24

Carscw

Carscw

Fish said:
Before all of my "haters" start pile driving me, I just would like to know what the date code was, so I could know whether or not you need to change your point ignition over to electronic.......
Click to expand...

Did not know you had haters.


#25

H

hatteras451

Fish said:
OK no points, but did you look at the bowl on the tank? Rust?
Click to expand...

Yes and no rust..I cleaned the tank when I disassembled and inspected for rust..


#26

H

hatteras451

mechanic mark said:
http://www.briggsandstratton.com/~/...on_troubleshooting_detail_reference_guide.pdf
Click to expand...

Thanks for the guide!


Footer Links 1

Top